Thread cutting mechanism for lockstitch sewing machines



May 19, 1970 IA.HEIMANN mL 3,512,491

THREAD CUTTING MECHANISM FOR LOCKSTITCH SEWING MACHINES Filed Sept. 2'7, 1968 2 Sheets-Sheet 1 Fig. 7

A 170 (may Fig. 2 'NVENTORS:

May 19, 1970 3,512,491

THREAD cuwwme MECHANISM FOR LOGKSTIICH SEWING MACHINES Filed Sept. 27, 1968 2 Sheets-Sheet 2 or R 0 TI N E V W EWI/l/l/l/l/Il/I/ 41 M0 #n/wmw, #0917 7/1/5115 W/L FR/Efl J'T/wrn MzJ/W/ Jame 4. 9 191912105) United States Patent 3,512,491 THREAD CUTTING MECHANISM FOR LOCKSTITCH SEWING MACHINES Alfred Heimann, Senne, Horst Thiele, Ubbedissen, and Wilfried Strothmann, Amshausen, Germany, assignors to Kochs Adlernahmaschinen Werke AG, Bieiefeld, Germany Filed Sept. 27, 1968, Ser. No. 773,359 Claims priority, application Germany, Sept. 27, 1967, 1,660,916 Int. Cl. Db 65/00 U.S. Cl. 112-252 13 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION An object of the invention is the provision of an improved thread cutting mechanism for lockstitch sewing machines by means of which the bobbin thread may be drawn 0E before it is cut in the immediate proximity of the workpiece.

Another object of the invention is to provide a thread cutting mechanism for buttonhole lockstitch sewing machines having a rotating loop taker arranged above the throat plate, a reciprocating needle piercing the workpiece from below and a presser foot between the loop taker and the throat plate.

It is a further object of the invention to provide a thread cutting mechanism which is both simple in construction, and reliable in operation, and which can be embodied also in conventional sewing machines.

There are already known lockstitch sewing machines provided with an arcuate thread catcher disposed close to the outer surface of, and rotatable coaXially with the loop taker for catching either only'the bobbin thread or the bobbin thread and a projecting end of the needle thread and supplying the thread or the threads to a stationary counterknife, arranged laterally of the stitch hole for the needle.

These thread cutting devices are described in German Pat. 353,627 to Duerkopp, of Sept. 8, 1918, U.S. Pat. 3,173,392 to Hedegaard, entitled Thread Trimming Mechanism for Lockstitch Sewing Machines, U.S. Pat. 3,173,393 to H. Adam, entitled Thread Cutting Mechanism for Lockstitch Sewing Machines.

These thread cutting mechanisms are not suitable for cutting the threads in the immediate proximity of a workpiece, since the arrangement of the stationary counterknife laterally of the stitch hole does not permit the thread ends leading to the workpiece to be cut ofi as short as possible. This is necessary, however, when using a cutting device in an automatic lockstitch sewing machine for producing buttonholes in linen.

SUMMARY According to the invention, the above problems are solved substantially by the provision of a thread cutting device comprising an arcuate cutting blade mounted for concentric oscillation about the loop taker, a counterknife cooperating with the arcuate blade, and operating means for the cutting device, while the counterknife is mounted for oscillation with the loop taker and in a direction counter to the arcuate blade. The arcuate blade and the counterknife are carried by arcuate carriers having arcuate slots. A round guide element which is mounted about and encircles the rotating loop taker is provided to receive the carriers rotating in opposite directions to one another. The round guide is furnished with slits for receiving guide pins mounted in the oppositely rotating carriers.

The arcuate carrier carrying the arcuate blade is provided with a thread draw-off means, which is actuated prior to the thread cutting operation. A clearance is provided between the draw-off means and the inner side of the round guide, for receiving the thread before cutting.

The operating means for the cutting mechanism includes two levers, which are articulated to the carriers, and an actuating lever which is articulated to the free ends of the levers for displacing the carriers in opposite directions.

There is further provided a bobbin case retaining means which prevents the rotating loop taker from following the bobbin case and which serves as a guide for the two levers articulated to the carriers. For this purpose, distance pieces are arranged between the bobbin case retaining plate and that part of ths housing of the sewing machine which carries the rotating loop taker.

The counterknife cooperating with the arched blade is provided with a downwardly extending projection for raising the blade against the counterknife before the beginning of the cutting action.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation showing the rotating loop taker, the bobbin case retaining plate and the thread cutting mechanism;

FIG. 2 is a section taken approximately on line 'IIII of FIG. 1;

FIG. 3 is a view similar to FIG. 1, but without the bobbin case retaining plate;

FIG. 4 is a view similar to FIG. 3, showing the thread cutting mechanism in another position, without the loop taker;

FIG. 5 is an enlarged part of the elevational view shown in FIG. 4;

FIG. 6 is a section taken on line VIVI of FIG. 5 and FIG. 7 shows the round guide for the carriers in a perspective view.

DESCRIPTION OF THE PREFERRED EMBODIMENT A loop taker shaft 2, carrying the rotating loop taker 3 is pivoted in the arm 1 (FIGS. 1 and 2) of a sewing machine. The bobbin case carrier 5 receiving the bobbin case 4 is provided with a bobbin case retaining plate 6 to prevent the rotating loop taker 3 from following it.

A round guide 7, arranged coaxially to and encircling the loop taker 3, is secured to the arm l by means of screws 8. The round guide 7 is provided with slits 12 for slidably receiving guide pins 13, which are inserted in two arcuate carriers 10, 11, formed with an arcuate slot 9. In these slots 9, the carriers 10, 11 are slidably mounted in the slots 9 of the guide 7.

An arcuate blade 14 is secured to the first carrier 10. The second carrier 11 is pro-vided with a counterknife 16 having an oblique cutting edge 17 and a projection 18 extending downwards for raising the arcuate blade 14 against the counterknife 16.

The first carrier 10 is formed with an arcuate thread draw-off means 19. Between it and the round guide 7 there is provided a clearance 20 (FIG. for receiving the bobbin thread 21, which comes from a bobbin 22, indicated by a dotted line in FIG. 5.

A clearance 23 is provided in the round guide 7 to permit the passage of the needle 24 piercing a workpiece 28 from below. The workpiece 28 lying upon a throat plate 25 and a fabric carrier plate 26 is pressed upon the throat plate 25 by a presser foot 27.

Two levers 30, 31 are pivoted to the carriers 10, 11 by means of shoulder studs 29. The free ends of both levers 30, 31 are articulated to a plug 32, which is a part of an actuating lever 33. The levers 30, 31 are slidably guided between the arm 1 and the bobbin case retaining plate 6, which is secured to the arm 1, distance pieces 34 (FIG. 2) secured by means of screws 35 being provided therebetween.

The operation of the above described thread cutting mechanism is as follows:

To cut the bobbin thread 21 it is necessary to press down the actuating lever 33 while the needle 24 (FIG. 3) is out of the throat plate 25. The carriers and 11 on the round guide 7 are thereby rotated counter toone another by the levers 30, 31. First the thread draw-01f means 19 engages the bobbin thread 21 for drawing off a length of thread from the bobbin 22, which is sufiicient to begin the next stitch formation (FIG. 5). Next, the bobbin thread 21 is cut ofi by the arcuate blade 14 and the counterknife 16, in the path of motion of the needle 24.

It will be noted that the bobbin thread 21 will be cut in the immediate proximity of the workpiece 28.

In the foregoing the invention has been described with reference to a lockstitch sewing machine having a reciprocating needle piercing the workpiece from below, and a rotating loop taker arranged above the throat plate. It will be evident, however, that the invention may also be employed in a lockstitch sewing machine of conventional construction, in which the needle pierces the workpiece from above, while the rotating loop taker is arranged below the throat plate.

Further it is conceivable that, if the thread draw-off means were formed in such a manner that it could seize the projecting end of the needle thread loop which leads to the workpiece, but not the end leading to the needle, the thread mechanism would be suitable to cut the bobbin thread as well as the needle thread in the immediate proximity of the workpiece.

Other modifications and variations as well as the substitution of equivalent elements and parts for those shown herein, may be made without departing from the broader scope and spirit of the invention, as set forth in the appended claims. The specification and drawings are accordingly to be regarded in an illustrative rather than in a restrictive sense.

What we claim is:

1. In combination with a lockstitch sewing machine having a cylindrical rotating loop taker, a throat plate and a reciprocating needle, a thread cutting mechanism comprising: an arcuate cutting blade mounted for oscillation concentrically about said loop taker, a counterknife cooperating with said arcuate cutting blade, and operating means for said cutting means, said counterknife being mounted for oscillation concentrically with said loop taker in a counter direction to said arcuate cutting blade.

2. In a thread trimming mechanism as claimed in claim 1, a first arcuate carrier carrying said arcuate cutting blade, a second arcuate carrier carrying said counterknife coacting with said cutting blade, said carriers having an arcuate slot and a round guide element mounted coaxially with and encircling said rotating loop taker, for slidably receiving said carriers, said carriers being rotatably counter to one another.

3. In a thread trimming mechanism as claimed in claim 1, a first arcuate carrier carrying said arcuate cutting blade, a second arcuate carrier carrying said counterknife coacting with said cutting blade, said carriers having an arcuate slot, and a round guide element mounted coaxially with and encircling said rotating loop taker, for slidably receiving said carrier rotatable counter to one another, said first arcuate carrier having a thread drawotf means actuable prior to the thread cutting operation.

4. 'In a thread trimming mechanism as claimed in claim 1, a first arcuate carrier carrying said arcuate cutting blade, a second arcuate carrier carrying said counterknife coacting with said arcuate cutting blade, said carriers having an arcuate slot, and a round guide mounted coaxially with and encircling said rotating loop taker, said round guide provided with slots for receiving guide pins secured in said carriers rotatable counter to one another, said first arcuate carrier having a thread drawoff means actuable prior to the thread cutting operation, and a clearance between said draw-ofl? means and the inner side of said round guide, for receiving said thread.

5. In a thread trimming mechanism as claimed in claim 1, a first arcuate carrier carrying said arcuate blade, at second arcuate carrier carrying said counterknife coacting with said arcuate cutting blade, said carriers having an arcuate slot, and a round guide element mounted co. axially with and encircling said rotating loop taker, said round guide element provided with slits for receiving guide pins in said carriers rotatable counter to one another, said first arcuate carrier having a thread drawoiT means actuable prior to the thread cutting operation and a clearance between said draw-off means and the inner side of said round guide element, for receiving said thread, said operating means for said cutting mechanism including a pair of levers articulated to said carriers, and an actuating lever for said pair of levers articulated to said carriers, for movement in contrarotating direction, the free ends of said pair of levers being articulated to said actuating lever.

6. In a thread trimming mechanism as claimed in claim 5, a bobbin case retaining means for preventing said rotating loop taker from following said bobbin case and for guiding said pair of levers articulated to said carriers.

7. In a thread trim-imng mechanism as claimed in claim 5, a bobbin case retaining plate for preventing said rotation loop taker from following said bobbin case and for guiding said two levers articulated to said carriers and distance pieces disposed between said bobbin case retaining plate and a part of the housing of said sewing machine carrying said rotating loop taker, for forming a guide for said levers.

8. In a thread trimming mechanism as claimed in claim 1, wherein said counterknife cooperating with said cutting blade is provided with a downwardly extending projection, for raising said cutting blade against said counterknife before beginning the cutting action.

9. In combination with a lockstitch sewing machine having a cylindrically rotating loop taker, a reciprocating needle piercing a workpiece from below and a throat plate, a thread cutting mechanism comprising: an arcuate cutting blade mounted for oscillation concentrically with said loop taker, a counterknife cooperating with said arcuate cutting blade, and operating means for said cutting mechanism, said counterknife being mounted for oscillation concentrically with said loop taker and counter to the rotation of said arcuate cutting blade.

10. In combination with a lockstitch sewing machine for sewing buttonholes having a cylindrically rotating loop taker, a reciprocating needle piercing a workpiece :from below, a thread drawing and cutting mechanism for the bobbin thread comprising: an arcuate cutting blade mounted for oscillation concentrically with said loop taker, a counterknife cooperating with said arcuate cutting blade, and operating means for said cutting device, said counterknife being mounted for oscillation concentrically with said loop taker and counter to the rotation of said arcuate cutting blade.

11. In a thread trimming mechanism as claimed in claim '10, a first arcuate carrier carrying said arcuate cutting blade, a second arcuate carrier carrying said counterknife, coacting with said arcuate cutting blade, said carriers having an arcuate slot, a round guide element mounted coaxially with and encircling said rotating loop taker, said round guide element having slits for receiving guide pins mounted in said carriers, said first arcuate carrier having a thread draw-off means actuable prior to the thread cutting operation and a clearance between said drawoff means and the inner side of said round guide element, for receiving said looper thread, said operating means for said cutting device including a pair of levers articulated to said carriers, an actuating lever for said pair of levers articulated to said carriers for movement counter direction to one another, the free ends of said levers being articulated to said actuating lever.

12. In a thread trimming mechanism as claimed in claim 11, a bobbin case retaining plate for preventing said rotating loop taker from following said bobbin case 6 and for guiding said pair of levers articulated to said carriers, distance pieces disposed between said bobbin case retaining plate and a part of the housing of said sewing machine carrying said rotating loop taker, for forming a guide for said levers.

I13. In a thread trimming mechanism as claimed in claim 10, wherein said counterknife cooperating with said cutting blade is provided with a downwardly extending projection, for raising said cutting blade upon said counterknife before the cutting action.

References Cited UNITED STATES PATENTS 3,139,849 7/1964 Cohen et a1. 112252 3,173,392 3/ 1965 Hedegaard 112-252 3,173,393 3/1965 Adam 112-252 3,386,402 6/1968 Ross 112-252 ALFRED R. GUEST, Primary Examiner 

